Field of the Invention
The present invention relates to a power saving technique for an image forming apparatus connected to a network via a communication section.
Description of the Related Art
Conventionally, there has been known an image forming apparatus connected to a network via a communication device, such as a NIC (Network Interface Card). In general, the image forming apparatus of this type has operating power modes, i.e. a normal power mode and a power saving mode smaller in power consumption than the normal power mode. When the image forming apparatus shifts from a normal operation state in which it is operated in the normal power mode, to a power saving state in which it is operated in the power saving mode, a communication speed is sometimes changed in order to reduce as much electric power being used as possible.
For example, in the power saving state, compared with the normal operation state, the communication speed of a network communication link between the image forming apparatus and a counter device (switching device such as a HUB) as a communication partner is changed to a lower speed. This is because as the communication speed of the network communication link is higher, a larger amount of power is consumed. In general, in the normal operation state, the communication is performed at 1 Gbps (Giga bits/sec) or 100 Mbps (Mega bits/sec) full-duplex. On the other hand, in the power saving state, the communication speed is changed to 10 Mbps half-duplex, whereby the power consumption in the power saving state is reduced.
In a case where a network packet e.g. of a print job is received in the power saving state, the image forming apparatus returns from the power saving state to the normal operation state, and then performs print processing. Packets transmitted via the network to the image forming apparatus are sometimes those of large-volume data, and hence it is necessary to perform higher-speed communication after the image forming apparatus is returned to the normal operation state. This requires the communication speed of the network communication link in the power saving state to be returned to a higher communication speed than in the normal operation state, and a technique meeting the requirement is known (Japanese Patent Laid-Open Publication No. 2014-90360).
To change the communication speed of the network communication link, it is necessary to temporarily disconnect the communication link whenever the speed is changed, and establish the communication link again at a changed speed. In general, when a communication link is established, there is a case where it takes time to establish the communication link depending on the compatibility between the image forming apparatus and a counter device. Further, depending on a network through which a communication link is established, it sometimes takes time to establish the communication link before a counter device improves the network environment using a spanning tree protocol. In a case where a print request is received when in the power saving state, the image forming apparatus returns to the normal operation state capable of performing print processing, and waits for the communication link to be established before starting to receive print data transmitted subsequently. This can lower the overall performance of the print processing, and depending on the case, print data cannot be received, and communication connection with a terminal having issued the print request can time out.
On the other hand, there has been proposed a method of maintaining the speed of a communication link in the normal operation state without changing the same, when shifting the image forming apparatus to the power saving state. According to this method, a larger amount of power is consumed even in the power saving state since the high-speed communication link is maintained. However, on the other hand, when the image forming apparatus returns to the normal operation state, it is possible to prevent network processing performance from being degraded, since it is unnecessary to temporarily disconnect the communication link so as to change the speed thereof.
More specifically, when the communication speed of the network communication link is lowered when the image forming apparatus is shifted to the power saving state, it is possible to improve power saving effects, but time taken for print processing is adversely affected since it takes time for the image forming apparatus to return to the normal operation state. On the other hand, when the image forming apparatus is shifted to the power saving state while maintaining the communication speed of the network communication link in the normal operation state, it is possible to reduce wasteful time in print processing which is wasted during returning the image forming apparatus to the normal operation state, but this results in reduced power saving effects (power saving efficiency). As described above, depending on a user of the image forming apparatus who has made the print request or office environments, it is impossible to univocally determine whether to give priority to power saving or to print processing speed including network processing performance, and which of the two choices is appropriate. Particularly, it is sometimes inappropriate to uniformly determine the priority regardless of user's will.